Electrochromic (EC) devices are being increasingly used for self dimming automotive mirrors and have been suggested for many different applications. Many of these devices are made by introducing a fluid between a cavity formed by perimeter bonding of two spaced apart substrates. The substrates are largely coplanar, i.e., the gap between the two substrates is uniform, even if the device (and the substrates) has curvature. The substrate surfaces facing inside the cavity are coated with conductive coatings. This fluid may remain as a liquid in the finished device or it is solidified after the cavity has been filled. In electrooptical devices including electrochromic devices, at least one electrically conductive coating is deposited on both the substrates, and at least one of which is transparent. Additional coatings may be deposited depending on the nature of construction and the device properties required. The perimeter sealant has one or more holes (or the substrates has one or more holes) through which the fluid (which forms the electrolyte in an EC device) is introduced and then these hole(s) are plugged (or sealed). The empty cavities with sealed perimeter are first prepared, and in a later step the fluid is introduced to fill the cavity. The introduction of the fluid is typically done by vacuum backfilling (e.g., see U.S. Pat. No. 5,140,455) or by an injection process (see U.S. Pat. No. 5,856,211 and published U.S. patent application 20090095408). The uniform gap between the two substrates is controlled by incorporating spacer beads in the perimeter sealant. However, this method does not work too well if the surface area of the device increases, as depending on the substrate rigidity the substrates may sag towards the center of the device and reduce the gap. It is then preferred that some spacers be added within the cavity to avoid this issue. In addition, in some curved devices, introducing spacer beads in the gap also helps in maintaining uniform spacing between the two substrates. These spacers are typically spherical or near spherical beads. These spacers interfere with clear vision as typically their refractive index (RI) is not the same as that of the electrolyte. One of the objectives is to disclose materials and schemes to make spacers and electrolytes with specific optical properties to overcome this problem.
If the RI of the material in the gap (e.g., the electrolyte layer in an electrochromic device) and the spacer material is not matched, then these spacers are visible and can be objectionable to a viewer. Matching means RI of the two materials to be within 0.05 RI units and more preferably within 0.002 RI units or better. In addition, unless mentioned otherwise RI in this disclosure refers to the real part of the refractive index in case complex RI notation is used. This becomes more of a problem with increasing gap, i.e., with larger spacers. The commercial EC automotive mirror devices have at least one electrochromic dye in the electrolyte and are self bleaching, i.e., when the power to color these devices is removed, they self bleach over a period of time. In such devices, for a given electrolyte composition, one has to usually increase the cell gap (or the conductivity of the conductive electrodes) with increasing device size so that the cell colors uniformly all over the area. This increase in gap reduces the self bleach reaction (also called back reaction), and ensures that the resistive potential drop from the edges (where highly conductive busbars are located) to the center of the device is small. It is the potential on the electrodes across the cell gap that controls the level of coloration. Furthermore, many of the EC mirrors use increasing cell gap with increasing mirror size (e.g., exterior automotive mirrors), where such spacers increase in visibility. This is also true for windows which are large in area, and windows using this type of construction are now being used for aircrafts. As an example glass spacers have an average refractive index (RI) of about 1.52 in the visible spectrum. Many devices using mainly propylene carbonate will have the electrolyte RI of about 1.42.
Many of the EC mirrors are now integrated with displays. These displays are assembled on the rear of the back substrate, and these are viewed from the front side. The mirror coating (typically on the third surface) is partially transmissive to allow these displays to be seen when these are powered. When the spacing between the substrates is large and spacers are used within the cavity, such spacers in the EC cells may interfere with the clarity of these displays as they scatter light due to the mismatch of their RI to that of the electrolyte. Active displays are typically provided in EC mirrors for conveying additional information (U.S. Pat. No. 4,882,565). Active displays in this context are those which are either capable of changing the information being displayed or they may be turned-off or turned-on. These displays may be in the mirror casing or in the mirror area. In interior mirrors the display may provide information on direction where the vehicle is headed (compass), amount of gas remaining, tire pressure, inside and/or outside temperature, internet communicated information, any warning or status signals such as open door, safety bag, videos of the rear interior car cabin, videos of rear vision while backing, taxi fare, etc. The displays in the outside mirror may provide blind spot information for the driver, or the turn signals for those cars in the vicinity of the vehicle without distracting the driver, directions from a GPS system and so forth.
Another novel way of incorporating partially transmissive reflectors is disclosed in this invention. This is done by using reflective coatings which are partially transmissive on the fourth surface, which is then combined with a protective polymeric coating which is transparent rather than the opaque paint that has been typically used to protect the fourth surface reflective coatings.
Thus, there is a preference from the automakers to reduce the optical distraction from these spacers in such mirrors. One of the method that has been suggested is to incorporate spacers within the cavity to hold a uniform gap when the cavity is formed, and as the cavity is filled with the fluid, the spacers can dissolve in this fluidic medium. Such methods are well described in U.S. Pat. Nos. 5,910,854, 7,643,200, 7,684,103, published U.S. patent application 20090027756. All of these patents and applications are incorporated herein by reference. U.S. Pat. Nos. 5,910,854 and 7,643,200 describe the use of plastic or polymeric spacers that can be dissolved in the electrolytic fluid, and the others describe making spacers of soluble materials such as salts, electrochromic dyes and UV stabilizers. When spacers dissolve and the substrate rigidity is low, then it is easy to push the substrate towards the center of the device where the top substrate deforms and is pushed closer to the rear substrate thus decreasing the electrolyte gap locally and in the extreme case may even touch the rear substrate and result in shorting. This could be done with relatively low force if a user is trying to clean the device. Thus spacers in the active area are preferred when there is a possibility of this happening to improve the mechanical stability of the cell.
Further, when one has the ability to change and match the RI of the electrolyte to the other materials then it leads to additional benefits. For example, it is preferred that the EC devices in the dark state have low reflectivity, however, one of the reasons for increased reflectivity is the RI mismatch of the substrate and the other layers in the device. For EC mirrors, matching of the electrolyte layer RI to that of the front substrate along with judicious choice of the transparent conductor coating properties and thickness on this substrate leads to low reflectivity, which is also another objective of this invention. Permanent indicators or markings or indicia on the mirrors have been traditionally etched, e.g., “Objects are closer than they appear on the mirror” or “Heated” on convex mirrors. Since many of these were first surface chrome mirrors this etching was done by removing chrome. There are patents on how these are incorporated into EC mirrors. For example U.S. Pat. Nos. 5,682,267; 5,689,370 and 5,189,537. U.S. Pat. No. 5,189,537 describes that this may be formed by depositing a dielectric layer on one of the inwardly facing transparent conductors. This blocks out the EC activity in the local area, thus making the markings visible when the device colors. U.S. Pat. No. 5,682,267 describes that this may be done by etching one of the interior facing surfaces before depositing the transparent conductor. This causes the reflection change in the area of etch. U.S. Pat. Nos. 5,689,370 and 7,859,738 describe another method where a reflective conductor is deposited on one of the conductive surfaces facing the interior of the EC cavity. U.S. Pat. No. 7,738,155 describes use of conductive materials to be deposited on the transparent conductor which is deposited on the second surface. All these methods may be used for devices of this invention, which means with porous spacers or those displays and/or insignias which are described in the present invention.
Automotive mirrors are an important safety item, first these mirrors reduce the driver's distraction caused by manually adjusting the mirror to reduce glare, and also reducing any optical impairment where both of these can add significant time before a driver can react to an emergency situation. However, these mirrors are expensive and even after 20 years of their introduction these are only found in about 20% of the automobiles. Thus it would be desirable to reduce their cost to extend this benefit to a larger number of automobiles. Part of this cost arises from the electronics to control, power and provide better user interfaces for mirrors, and this innovation also addresses the ways such cost can be reduced by integrating many of the electronic components in the mirror case (which includes bezels) which are used to house the EC mirror element.
One issue with all of these passive indicators (e.g., insignias) is that either they have good visibility in the daytime (when the mirror is bleached and the ambient conditions are bright), or at night when the mirror is colored and the visibility is enhanced by a differential reflectivity or absorption when illuminated by another vehicle or another source. Those indices are desirable that can be seen in nighttime and during the daytime under multiple illumination or ambient conditions and whether the electrochromic mirror (only if it is an electrochromic mirror) is bleached or dark. Further in many situations it is desirable that these be observed not just by the driver of the car which has this insignia, but preferably by those people who are in the vicinity, such as drivers and passengers of other cars nearby. As discussed in detail such attributes can be imparted by incorporating insignias which use retroreflective properties and/or use luminescent materials.
Electrochromic mirrors in automobiles are typically hard wired to the power system of an automobile. In order to reduce the cabling complexity and cost especially for retrofit applications, it is desirable to provide power to these mirrors which does not require these cables.